Refinement of free structure parameters of a thin film when only one reflection is available

A procedure is described to exploit measurements for the refinement of free structure parameters if only a few (or even only one) reflections are available. The method is illustrated taking an epitaxial layer of Ga_0.5In_0.5P deposited on (001)GaAs as an example, where the number of accessible reflections is limited by geometrical conditions. Another complication with this material arises from the well known ordering phenomenon, which occurred in a small part of the layer only. It is shown that the energy dependence of DAFS (diffraction anomalous fine structure) intensity is still sufficiently sensitive to values of free structure parameters when the oscillating part of the DAFS/XAFS (X-ray absorption fine structure) structure factor is ignored for evaluation of intensity. This facilitates evaluation of DAFS intensities considerably by avoiding time-consuming analysis of fine structure.